The invention relates to machine elements and mechanisms, but more particularly, the invention relates to endless power transmisson belts with plural driving surfaces of the V-type.
Power is transmitted between a belt and a sheave as oppositely facing driving surfaces of the belt are wedged in a V-groove of the sheave by means of belt tension. The outside edges of the tensile member are supported by opposite faces that define the sheave groove while the center portion of the tensile member receives no direct support other than by belt construction per se. Thus, the mid-portion of the tensile member is subject to being disposed at a point radially inward of the outside edge portions of the tensile member which overstresses the outside edge of the tensile member.
As was early recognized and disclosed in U.S Pat. Nos. 2,194,833 and 2,292,290, the tensile member may be constructed transversely convex with the convex side towards the outer surface of the belt so that when the belt is tensioned in a sheave, the mid-portion of the tensile member is not easily displaced to a point radially inward of the outside edges of the tensile member. Thus, the convex construction helps distribute a tensile load to the mid-portion of the tensile member.
The problem of distributing the tensile load to the mid-portion of the tensile member becomes greater as the ratio of belt width to belt thickness is increased or if belt tension is increased. The problem is particularly associated with variable speed type belts where a large belt width to belt thickness ratio is required to effect a predetermined speed ratio change in a sheave. Convexly arching the tensile member is insufficient to overcome the movement of the mid-portion of the tensile member to a radially inward point under high belt tensions.